In a nonhallucinatory moment he bought a bedroom fan to blow away the toxic gas.
Cooper was diagnosed with Lewy Body Dementia, a form of progressive dementia that leads to a decline in thinking, reasoning and independent function, a result of microscopic deposits that damage brain cells over time.
An individual who has Lewy Body Dementia often suffers from recurrent, complex, visual hallucinations, typically well-formed and detailed.
When Judy Cooper heard about what had taken over her husband's life, she was shocked and, she admits, spooked.
"It's startling and very weird," she said. "(The visions were) like a self-fulfilling prophecy."
As she started reading a draft of her husband's book, she realized it included many autobiographical elements. The protagonists were lawyers, just like Jay. One of the lawyers was Jewish and extremely messy, much like the man she fell in love with more than 50 years ago.
And there is one scene in the book where one of Jay's characters, an attorney named David Gold, looks out a window and has a vision.
He sees an army of soldiers coming right at him.
Jay Cooper doesn't make much of the similarities between his book and his own life.
"It was a story, that's all," he says.
He tries to separate fact from fiction — even when he's having the worst, most frightening hallucinations.
"I cannot control the content of my vision," he says. "When it comes on, I can feel it come on. Getting through it, that's a different story."
For now, he can still tell himself this: "If you don't think it's real, it ain't real."
Even as he sees the vase on his table transform into a person who then turns around and looks at him, he slaps his own face and commands himself to "snap out of it."
At night, if he feels a vision coming on, he'll get on the floor and do 20 pushups. At 86, he says, that's not a bad deal.
In September, Cooper spoke at the 20th annual Southern California Alzheimer's disease Research Conference. There, participants shared their methods of coping with various forms of dementia.
As Cooper took the microphone, he told the audience: "I'd just like to say… Welcome to the Academy Awards!"
He was kidding of course, but making an important point: A sense of humor, he says, can help you get through the worst day.
"You've got to accentuate the positive."
On Dec. 15, 2012, "Hammurabi's Dagger" was published on Amazon.
When his wife brought him a copy of the yellow paperback, Cooper clutched it to his chest.
"I couldn't believe it," he said.
Then, smiling mischievously, he added:
"I thought, 'This is an illusion. It must be!'"
To learn more: Information on Lewy Body Dementia can be found at lbda.org.